1. Field of the Invention
The present invention relates to new crystalline zeolite SSZ-57 and a method for preparing SSZ-57 using a N-butyl-N-cyclohexylpyrrolidinium cation, N-propyl-N-cycloheptylpyrrolidinium or N-butyl-N-cyclooctylpyrrolidinium cation as tempting agent.
2. State of the Art
Because of their unique sieving characteristics, as well as their catalytic properties, crystalline molecular sieves and zeolites are especially useful in applications such as hydrocarbon conversion, gas drying and separation. Although many different crystalline molecular sieves have been disclosed, there is a continuing need for new zeolites with desirable properties for gas separation and drying, hydrocarbon and chemical conversions, and other applications. New zeolites may contain novel internal pore architectures, providing enhanced selectivities in these processes.
Crystalline aluminosilicates are usually prepared from aqueous reaction mixtures containing alkali or alkaline earth metal oxides, silica, and alumina. Crystalline borosilicates are usually prepared under similar reaction conditions except that boron is used in place of aluminum. By varying the synthesis conditions and the composition of the reaction mixture, different zeolites can often be formed.
The present invention is directed to a family of crystalline molecular sieves with unique properties, referred to herein as xe2x80x9czeolite SSZ-57xe2x80x9d or simply xe2x80x9cSSZ-57xe2x80x9d. Preferably, SSZ-57 is obtained in its borosilicate form, but the present novel zeolite can be synthesized in both the borosilicate or aluminosilicate phase. The term xe2x80x9cborosilicatexe2x80x9d refers to a zeolite containing oxides of both boron and silicon. The term xe2x80x9caluminosilicate refers to a zeolite containing oxides of both aluminum and silicon.
In accordance with this invention, there is provided a zeolite having a mole ratio greater than about 20 of an oxide selected from silicon oxide, germanium oxide and mixtures thereof to boron oxide or a combination of boron oxide and aluminum oxide, gallium oxide, indium oxide, titanium oxide or a mixture thereof and having, after calcination, the X-ray diffraction lines of Table 3 below.
The present invention further provides such a zeolite having a composition, as synthesized and in the anhydrous state, in terms of mole ratios as follows:
wherein Y is silicon, germanium or a mixture thereof; W is boron or a combination of boron and aluminum, gallium, indium, titanium or a mixture thereof; M is an alkali metal cation, alkaline earth metal cation or mixtures thereof; n is the valence of M (i.e., 1 or 2); c is 1 or 2; d is 2 when c is 1 (i.e., W is tetravalent) or d is 3 or 5 when c is 2 (i.e., d is 3 when W is trivalent or 5 when W is pentavalent); and Q comprises a N-butyl-N-cyclohexylpyrrolidinium cation, N-propyl-N-cycloheptylpyrrolidinium cation or N-butyl-N-cyclooctylpyrrolidinium.
In accordance with this invention, there is also provided a zeolite prepared by thermally treating a zeolite having a mole ratio of an oxide selected from silicon oxide, germanium oxide and mixtures thereof to boron oxide or a combination of boron oxide and aluminum oxide, gallium oxide, indium oxide, titanium oxide or a mixture thereof greater than about 20 at a temperature of from about 200xc2x0 C. to about 1100xc2x0 C., the thus-prepared zeolite having the X-ray diffraction lines of Table 3 below. The present invention also includes this thus-prepared zeolite which is predominantly in the hydrogen form, which is prepared by ion exchanging with an acid or with a solution of an ammonium salt followed by a second calcination.
Also provided in accordance with the present invention is a method of preparing a crystalline material comprising an oxide selected from silicon oxide, germanium oxide and mixtures thereof and boron oxide or a combination of boron oxide and aluminum oxide, gallium oxide, indium oxide, titanium oxide or a mixture thereof, said method comprising contacting under crystallization conditions sources of said oxides and a tempting agent comprising a N-butyl-N-cyclohexylpyrrolidinium cation, N-propyl-N-cycloheptylpyrrolidinium cation or N-butyl-N-cyclooctylpyrrolidinium.
The present invention comprises a family of crystalline zeolites designated herein xe2x80x9czeolite SSZ-57xe2x80x9d or simply xe2x80x9cSSZ-57xe2x80x9d.
In preparing SSZ-57 zeolites, a N-cyclohexyl-N-butylpyrrolidinium ammonium cation, N-propyl-N-cycloheptylpyrrolidinium cation or N-butyl-N-cyclooctylpyrrolidinium is used as a crystallization template. In general, SSZ-57 is prepared by contacting an active source of an oxide selected from silicon oxide, germanium oxide and mixtures thereof and boron oxide or a combination of boron oxide and aluminum oxide, gallium oxide, indium oxide, titanium oxide or a mixture thereof with the tempting agent.
SSZ-57 is prepared from a reaction mixture having the composition shown in Table A below.
where Y, W, Q, M and n are as defined above, and a is 1 or 2 and b is 2 when a is 1 (i.e., W is tetravalent) or b is 3 when a is 2 (i.e., W is trivalent).
In practice, SSZ-57 is prepared by a process comprising:
(a) preparing an aqueous solution containing sources of at least one oxide capable of forming a crystalline molecular sieve and the N-butyl-N-cyclohexylpyrrolidinium cation, N-propyl-N-cycloheptylpyrrolidinium cation or N-butyl-N-cyclooctylpyrrolidinium in the presence of an anionic counterion which is not detrimental to the formation of SSZ-57;
(b) maintaining the aqueous solution under conditions sufficient to form crystals of SSZ-57; and
(c) recovering the crystals of SSZ-57.
Accordingly, SSZ-57 may comprise the crystalline material and the tempting agent in combination with metallic and non-metallic oxides bonded in tetrahedral coordination through shared oxygen atoms to form a cross-linked three dimensional crystal structure. The metallic and non-metallic oxides comprise an oxide selected from silicon oxide, germanium oxide and mixtures thereof and boron oxide or a combination of boron oxide and aluminum oxide, gallium oxide, indium oxide, titanium oxide or a mixture thereof.
Typical sources of silicon oxide include silicates, silica hydrogel, silicic acid, fumed silica, colloidal silica, tetra-alkyl orthosilicates, and silica hydroxides. Boron, as well as aluminum, gallium, germanium, titanium, and indium can be added in forms corresponding to their silicon counterparts.
A source zeolite reagent may provide a source of boron. In most cases, the source zeolite also provides a source of silica. The source zeolite in its dealuminated or deboronated form may also be used as a source of silica, with additional silicon added using, for example, the conventional sources listed above. Use of a source zeolite reagent as a source of alumina for the present process is more completely described in U.S. Pat. No. 5,225,179, issued Jul. 6, 1993 to Nakagawa entitled xe2x80x9cMethod of Making Molecular Sievesxe2x80x9d, the disclosure of which is incorporated herein by reference.
Typically, an alkali metal hydroxide and/or an alkaline earth metal hydroxide, such as the hydroxide of sodium, potassium, lithium, cesium, rubidium, calcium, and magnesium, is used in the reaction mixture; however, this component can be omitted so long as the equivalent basicity is maintained. The tempting agent may be used to provide hydroxide ion. Thus, it may be beneficial to ion exchange, for example, the halide for hydroxide ion, thereby reducing or eliminating the alkali metal hydroxide quantity required. The alkali metal cation or alkaline earth cation may be part of the as-synthesized crystalline oxide material, in order to balance valence electron charges therein.
The reaction mixture is maintained at an elevated temperature until the crystals of the SSZ-57 zeolite are formed. The hydrothermal crystallization is usually conducted under autogenous pressure, at a temperature between 100xc2x0 C. and 200xc2x0 C., preferably between 135xc2x0 C. and 160xc2x0 C. The crystallization period is typically greater than 1 day and preferably from about 3 days to about 20 days.
Preferably, the zeolite is prepared using mild stirring or agitation.
During the hydrothermal crystallization step, the SSZ-57 crystals can be allowed to nucleate spontaneously from the reaction mixture. The use of SSZ-57 crystals as seed material can be advantageous in decreasing the time necessary for complete crystallization to occur. In addition, seeding can lead to an increased purity of the product obtained by promoting the nucleation and/or formation of SSZ-57 over any undesired phases. When used as seeds, SSZ-57 crystals are added in an amount between 0.1 and 10% of the weight of silica used in the reaction mixture.
Once the zeolite crystals have formed, the solid product is separated from the reaction mixture by standard mechanical separation techniques such as filtration. The crystals are water-washed and then dried, e.g., at 90xc2x0 C. to 150xc2x0 C. for from 8 to 24 hours, to obtain the as-synthesized SSZ-57 zeolite crystals. The drying step can be performed at atmospheric pressure or under vacuum.
SSZ-57, as prepared, has a mole ratio of an oxide selected from silicon oxide, germanium oxide and mixtures thereof to boron oxide or a combination of boron oxide and aluminum oxide, gallium oxide, indium oxide, titanium oxide or a mixture thereof greater than about 20; and has the X-ray diffraction lines of Table I below. SSZ-57 further has a composition, as-synthesized and in the anhydrous state, in terms of mole ratios, shown in Table B below.
where Y, W, c, d, M, n and Q are as defined above.
SSZ-57 can be made essentially aluminum free, i.e., having a silica to alumina mole ratio approaching ∞. A method of increasing the mole ratio of silica to alumina is by using standard acid leaching or chelating treatments. However, essentially aluminum-free SSZ-57 can be synthesized directly using essentially aluminum-free silicon and boron sources. SSZ-57 is generally prepared directly as a borosilicate.
Lower silica to alumina ratios may also be obtained by using methods which insert aluminum into the crystalline framework. For example, aluminum insertion may occur by thermal treatment of the zeolite in combination with an alumina binder or dissolved source of alumina. Such procedures are described in U.S. Pat. No. 4,559,315, issued on Dec. 17, 1985 to Chang et al.
It is believed that SSZ-57 is comprised of a new framework structure or topology which is characterized by its X-ray diffraction pattern. SSZ-57 zeolites, as-synthesized, have a crystalline structure whose X-ray powder diffraction pattern exhibit the characteristic lines shown in Table 1 and is thereby distinguished from other zeolites.
(b) The X-ray patterns provided are based on a relative intensity scale in which the strongest line in the X-ray pattern is assigned a value of 100: W(weak) is less than 20; M(medium) is between 20 and 40; S(strong) is between 40 and 60; VS(very strong) is greater than 60.
The complete X-ray diffraction pattern of a boron SSZ-57 zeolite is shown in Table 2 below:
After calcination, the SSZ-57 zeolites have a crystalline structure whose X-ray powder diffraction pattern include the characteristic lines shown in Table 3:
The complete X-ray diffraction pattern for an SSZ-57 calcined zeolite is shown in Table 4:
The X-ray powder diffraction patterns were determined by standard techniques. The radiation was the K-alpha/doublet of copper. The peak heights and the positions, as a function of 2 Theta where Theta is the Bragg angle, were read from the relative intensities of the peaks, and d, the interplanar spacing in Angstroms corresponding to the recorded lines, can be calculated.
The variation in the scattering angle (two theta) measurements, due to instrument error and to differences between individual samples, is estimated at xc2x10.15 degrees.
The X-ray diffraction pattern of Table 1 is representative of xe2x80x9cas-synthesizedxe2x80x9d or xe2x80x9cas-madexe2x80x9d SSZ-57 zeolites. Minor variations in the diffraction pattern can result from variations in the silica-to-boron or silica-to-alumina mole ratio of the particular sample due to changes in lattice constants. In addition, sufficiently small crystals will affect the shape and intensity of peaks, leading to significant peak broadening.
Representative peaks from the X-ray diffraction pattern of calcined SSZ-57 are shown in Table 3. Calcination can also result in changes in the intensities of the peaks as compared to patterns of the xe2x80x9cas-madexe2x80x9d material, as well as minor shifts in the diffraction pattern. The zeolite produced by exchanging the metal or other cations present in the zeolite with various other cations (such as H+ or NH4+) yields essentially the same diffraction pattern, although again, there may be minor shifts in the interplanar spacing and variations in the relative intensities of the peaks. Notwithstanding these minor perturbations, the basic crystal lattice remains unchanged by these treatments.
Crystalline SSZ-57 can be used as-synthesized, but preferably will be thermally treated (calcined). Usually, it is desirable to remove the alkali metal cation by ion exchange and replace it with hydrogen, ammonium, or any desired metal ion. The zeolite can be leached with chelating agents, e.g., EDTA or dilute acid solutions, to increase the silica to alumina mole ratio. The zeolite can also be steamed; steaming helps stabilize the crystalline lattice to attack from acids.
The zeolite can be used in intimate combination with hydrogenating components, such as tungsten, vanadium molybdenum, rhenium, nickel cobalt, chromium, manganese, or a noble metal, such as palladium or platinum, for those applications in which a hydrogenation-dehydrogenation function is desired.
Metals may also be introduced into the zeolite by replacing some of the cations in the zeolite with metal cations via standard ion exchange techniques (see, for example, U.S. Pat. No. 3,140,249 issued Jul. 7, 1964 to Plank et al.; U.S. Pat. No. 3,140,251 issued Jul. 7, 1964 to Plank et al.; and U.S. Pat. No. 3,140,253 issued Jul. 7, 1964 to Plank et al.). Typical replacing cations can include metal cations, e.g., rare earth, Group IA, Group IIA and Group VIII metals, as well as their mixtures. Of the replacing metallic cations, cations of metals such as rare earth, Mn, Ca, Mg, Zn, Cd, Pt, Pd, Ni, Co, Ti, Al, Sn, and Fe are particularly preferred.
The hydrogen, ammonium, and metal components can be ion-exchanged into the SSZ-57. The zeolite can also be impregnated with the metals, or the metals can be physically and intimately admixed with the zeolite using standard methods known to the art.
Typical ion-exchange techniques involve contacting the synthetic zeolite with a solution containing a salt of the desired replacing cation or cations. Although a wide variety of salts can be employed, chlorides and other halides, acetates, nitrates, and sulfates are particularly preferred. The zeolite is usually calcined prior to the ion-exchange procedure to remove the organic matter present in the channels and on the surface, since this results in a more effective ion exchange. Representative ion exchange techniques are disclosed in a wide variety of patents including U.S. Pat. No. 3,140,249 issued on Jul. 7, 1964 to Plank et al.; U.S. Pat. No. 3,140,251 issued on Jul. 7, 1964 to Plank et al.; and U.S. Pat. No. 3,140,253 issued on Jul. 7, 1964 to Plank et al.
Following contact with the salt solution of the desired replacing cation, the zeolite is typically washed with water and dried at temperatures ranging from 65xc2x0 C. to about 200xc2x0 C. After washing, the zeolite can be calcined in air or inert gas at temperatures ranging from about 200xc2x0 C. to about 800xc2x0 C. for periods of time ranging from 1 to 48 hours, or more, to produce a catalytically active product especially useful in hydrocarbon conversion processes.
Regardless of the cations present in the synthesized form of SSZ-57, the spatial arrangement of the atoms which form the basic crystal lattice of the zeolite remains essentially unchanged.
SSZ-57 can be formed into a wide variety of physical shapes. Generally speaking, the zeolite can be in the form of a powder, a granule, or a molded product, such as extrudate having a particle size sufficient to pass through a 2-mesh (Tyler) screen and be retained on a 400-mesh (Tyler) screen. In cases where the catalyst is molded, such as by extrusion with an organic binder, the aluminosilicate can be extruded before drying, or dried or partially dried and then extruded.
SSZ-57 can be composited with other materials resistant to the temperatures and other conditions employed in organic conversion processes. Such matrix materials include active and inactive materials and synthetic or naturally occurring zeolites as well as inorganic materials such as clays, silica and metal oxides. Examples of such materials and the manner in which they can be used are disclosed in U.S. Pat. No.4,910,006, issued May 20, 1990 to Zones et al., and U.S. Pat. No. 5,316,753, issued May 31, 1994 to Nakagawa, both of which are incorporated by reference herein in their entirety.
SSZ-57 is useful in catalysts for hydrocarbon conversion reactions such as hydrocracking, dewaxing, isomerization and the like.